This invention relates to an automatic control device for earth working equipment.
When a grading or earth-pushing work is conducted with earth working equipment such as a bulldozer, it is necessary that the work is efficiently carried out without imposing overload to the vehicle body or the blade; however, in practice, it is difficult to do so.
In a conventional blade control method, a laser beam is emitted from a laser beam emitter set at a predetermined position of the vehicle, which has a reference height, and a laser beam receiver fixedly provided at a predetermined position of the blade or the like receives the laser beam thus emitted, thereby to obtain a height signal which is utilized to automatically control the height of the blade.
In another conventional blade control method, the bulldozer itself has a reference value, and the blade inclination angle is detected by means of a vertical gyroscope or an inclinometer, so that the blade height is automatically controlled in accordance with the difference between the detection value and the reference value.
However, the former method is disadvantageous in the following points: In a dusty place, or in a place where the ground vibrates, the laser beam is disturbed, and therefore the sufficient result cannot be obtained. In addition, the control device is considerably intricate, and accordingly, high in manufacturing cost.
The latter method is also disadvantageous in the following points: In the case where the vertical gyroscope is employed for the detection of the blade inclination angle, the vertical gyroscope itself is expensive, and is relatively low in durability against vibration. In the case where the inclinometer is employed, it is not expensive; however, it is affected by the acceleration and deceleration of the vehicle body. Therefore, when the vehicle speed is varied, it is impossible to control the blade.
In order to perform the blade control by detecting a load applied to the blade, a method is known in the art in which, for a wheel type vehicle such as motor grader or a motor scraper, the ratio in r.p.m. of the driving wheel to the driven wheel is detected to obtain a slip signal, which is utilized to control the vertical movement of the blade.
In this method, the detection is carried out after the load is increased to cause the driving wheel to slip. Therefore, the method is not applicable to a caterpillar type vehicle.
In the automatic blade control, the finish accuracy is greatly affected by the response speed. In the ordinary on-off control system, it is necessary to increase the dead zone to increase the response speed, but if the dead zone is increased, then hunting is caused. Therefore, in the ordinary on-off control system, the finish accuracy is lowered by increasing the response speed. Furthermore, in the ordinary on-off control system, it is necessary to decrease the response speed to increase the finish accuracy. Thus, the ordinary on-off control system suffers from the contradictory problem.
As is apparent from the above description, it is very difficult to automatically control the blade, and therefore almost all of earth working equipments such as bulldozers have no automatic blade control devices.
Accordingly, earth working operations such as those in pushing or leveling of earth are considerably difficult, and the operator must be highly skilled in the operation of the earth working equipment. As the working conditions are severe, the operator becomes considerably fatigued, which makes the work more difficult.